1.5°C WARMING LIMIT COULD PROTECT TWO-THIRDS OF ASIA’S GLACIERS

Two-thirds of Asia’s glaciers could survive to the end of the century if countries can limit average global warming to 1.5°C, according to a new study in the journal Nature.

Even if all greenhouse gas emissions were stopped today, 14% of the continent’s “iconic snowy landscape” would be lost by 2100, Carbon Brief reports. With no effort at all to curtail emissions, two-thirds of the glaciers’ expanse could be gone by that time. The range of possible futures will make a decisive difference for the 800 million people in Asia who depend on the glaciers for drinking water.

“The thousands of glaciers that are strung across the high mountains of Asia contain the largest store of permanent ice and permafrost outside of the North and South poles,” Carbon Brief explains. But “despite its snowy exterior, the mountainous region is expected to warm up at a faster pace than the surrounding low-lying land as global temperatures rise,” partly because the snow reflects more solar radiation back into the atmosphere than the darker earth beneath.

“As the glaciers retreat, they expose more of the dark, rocky ground beneath,” writes science correspondent Daisy Dunne. “This means the land then absorbs more of the sun’s radiation and heats up more quickly, melting more ice.”

As lead author Philip Kraaijenbrink told Dunne, “snow reflects a large part of the incoming radiation, up to 90%, which means it has a high albedo. And a high snowline consequently means that more energy stays at the Earth’s surface.”

The research team modelled glacier mass and melt under three different scenarios for future global warming, then compared the results with ice levels observed between 1996 and 2015. The more extreme the outcome, the more severely glacier loss will affect people in China, India, Nepal, Russia, and Kazakhstan.

“Currently, meltwater from the glaciers provides a relatively steady supply of water to the rivers during the annual melt season. This water is used for irrigation, drinking water, and hydropower,” Dunne writes. “Climate change could increase the rate of ice melt and, as a result, lead to a sharp increase in the supply of meltwater in the coming decades.”

Under the two more optimistic scenarios, Kraaijenbrink said, “peak meltwater” could occur as early as 2030.

“Glaciers store water in cold, often wet times of the year and release it during warm summer months when other sources of stream flow may be in short supply. This augmented supply of water, through glacier storage and runoff, can be critical when other sources are absent,” explained NASA scientist Dr. Alex Gardner, who was not involved in the study.

“To fully understand the implications of the projected glacier loss on future stream flows will require understanding the resultant change in river input, relative to other sources, upstream of dependent populations.”

The study also looked at the impact of large rocks and stones that are carried along by glaciers as they move through mountain valleys. “Depending on its thickness, this debris can either suppress or enhance ice melt,” Carbon Brief notes. “Thin debris accelerates melt because it absorbs more heat than debris-free ice. However, thick debris can act as a blanket buffer, protecting the ice beneath from changes in temperature.”

That dynamic might point to an opportunity to protect Asian glaciers by covering them with larger debris, Dunne writes. “However, this would be a very large undertaking,” Kraaijenbrink said, “and our efforts may be better aimed at reducing the causes of climate change and glacier mass loss.”